1. Field of the Invention
This invention pertains to a method for treating wells penetrated and completed in subterranean earth formations, and more particularly to a method for treating a petroleum containing formation in the immediate vicinity of the well so as to stabilize unconsolidated sand and prevent migration into or away from the well. Still more particularly, this invention pertains to a method for treating such wells with granular materials saturated with bitumen or bituminous or asphaltic petroleum, contacting the material with a liquid chlorinated hydrocarbon to cause precipitation of asphalt, and then introducing steam to solidify the bitumen and bind the sand grains together.
2. Prior Art and Background
Recovery of formation fluid such as petroleum from a subterranean formation is frequently difficult when the subterranean formation is comprised of one or more incompetent or unconsolidated sand layers or zones. The sand particles in the incompetent or unconsolidated sand zone move or migrate into the well bore during recovery of formation fluids from that zone, or sand particles move away from the well during injection of secondary or tertiary recovery fluids into the formation. In the instance of recovering the fluid from the formation, the movement of sand into the well bore can cause the well to cease production of fluids therefrom. Also, small sand particles can plug small openings and porous masses formed around the well bore for the purpose of restraining the flow of sand, such as screens or slotted liners which are frequently placed in wells for this purpose. Not only can fluid production be reduced or even stopped altogether, if sand particles flow through the well to the surface, considerable mechanical problems can result from passage of abrasive sand particles through pumps and other mechanical devices.
Many techniques have been described in the prior art for preventing or decreasing the flow of sand into well in a course of petroleum production, including the use of sand screens, filters, perforated or slotted liners, etc. around the well. These prior art attempts have been successful in some limited instances, but have not always been entirely satisfactory for a number of reasons. Mechanical devices usually restrain only the larger particle sand and are not completely effective for the purpose of restraining or preventing the flow of fine particles from the formation into the well and ultimately to the surface. Furthermore, the devices interfere with various types of completions and work over operations.
Recently, there have been introduced into the market place by numerous oil field companies, chemical compositions which bond the sand grains together with a resinous plastic material to form a permeable mass which effectively restrains the flow of sand particles from the formation. These methods involve injecting into a sand pack around the well bore, a polymerizable, resinous material, which is later caused to polymerize so as to consolidate formation sand or sand packed around the well for that purpose, to form the desired permeable barrier. Numerous difficulties have been encountered in commercial application and use of this technique, including the difficulty of achieving the even polymerization of the resinous material to the degree necessary to consolidate the sand particles while still maintaining the necessary permeability so that petroleum or other fluid may pass therethrough. Furthermore, the resinous materials are expensive. Recently, many tertiary recovery techniques involving the injection of steam or other fluids into the formation for the purpose of mobilizing viscous petroleum have been tried which impose a still greater burden on sand consolidation techniques, and has particularly caused problems with the plastic consolidation techniques which are sensitive to the high temperature, high pH aqueous fluids frequently employed in such processes. The resinous materials are frequently dissolved or degraded by contact with the hot alkaline fluids used in tertiary recovery processes.
U.S. Pat. Nos. 3,910,351 and 3,951,210 describe the treatment of unconsolidated petroleum bearing sand in a subterranean petroleum containing formation. These methods use liquid hydrocarbons such as butane, pentane or hexane, N-methyl-2-pyrrolidone and furfural to solubilize non-asphaltic fractions of the petroleum-sand mass surrounding the well bore. Test cores produced by methods using these liquid hydrocarbons have exhibited weakness in withstanding compressive forces.
In view of the foregoing discussion, it can be appreciated that there is a substantial, unfulfilled need for a sand control method capable of preventing the flow of unconsolidated sand particles into a well bore during periods of oil recovery or away from a well bore during periods of injection of fluids thereinto. More particularly, there is a need for inexpensive, reliable method of consolidating sand in a formation having an appreciable quantity of unconsolidated sand, which will result in the formation of a permeable mass that will not be adversely affected by subsequent contact with high temperature, alkaline fluid such as steam or caustic.
By the method of the present invention one is able to treat underground formations as to effect the solidation of granular materials such as sand or gravel into a permeable mass which will effectively restrain the movement of unconsolidated sand particles, which permeable mass will not be appreciably degraded by subsequent contact with hot alkaline fluids such as steam and/or caustic, and generally avoid many of the disadvantages of prior art methods, both mechanical and chemical.